Thermostat



May 12, 1942. c. R. PALMER THERMOS TAT Filed June 26, 1940 ATTORNEY.

Patented May 12, 1942 UNITED STATES PATENT OFFICE THERMOSTAT Charles R. Palmer, Glen Acres, Ohio Application June 26, 1940, Serial No. 342,510

2 Claims.

The invention relates to improvements in thermostats employing a capillary tube.

It is an object of the invention to provide a thermostat in the form of a sealed capillary tube, wherein the expansive fluid serves as a conductor, to maintain and control an electric-circuit, and adapted at a determined temperature to develop a pressure internal of the tube suffioient to shatter thefluid containing bulb of the tube and forcibly expel the fluid to break or open the electric circuit, thereby requiring tube replacement before the circuit can be re-established.

Another object of the invention is to provide a thermostat in the form of a capillary tube, wherein the expansive fluid is an electriccircuit conductor and controlling medium below a predetermined maximum degree of temperature, either internal or external of the tube; the expansion of the fluid at the maximum degree of temperature developing a pressure suflicient to shatter the tube and expel the fluid for an automatic electric circuit cut-off control.

Another object of the invention is to provide a non-variable thermostat in the form of a capillary tube for insertion in an electric circuit to disrupt the circuit at a predetermined degree of temperature, the tube of minimum size, simple and cheap in construction, and as a clip insertable in an electric circuit.

Another object of the invention is to provide a capillary tube thermostat in which the expansive and electro-conductive fluid is opposed by a vapor head pressure for shattering the tube and expelling the fluid by an excessive pressure developed at a determined degree of temperature.

It is a further object to constrict the bore of the tube near the egress end thereof and preferabl intermediate the contacts to decrease the velocity of the flow of the mercury during its expulsion to efiectively clear said end of the tube and a portion thereof between the contacts of all mercury to assure complete disconnection of the contacts.

Various other features and advantages of the invention will be more fully apparent from a description of the accompanying drawing, in which:

Figure 1 is a side elevation of the thermostat or electric circuit breaker in a mounted position and in an electric circuit.

Figure 2 is a central vertical section taken on line 2-2, Figure 1.

Figure 3 is a view similar to Figure 2, with the lower bulb portion of the tube shattered, and the electro-conducting expansive fluid expelled.

Figure 4 is a cross sectional view taken on the line 4-4, Figure 1.

Figure 5 is an enlarged cross sectional detail view, taken on line 5-5, Figure 2.

The thermostat in the present instance is in the form of a tube In of glass or other insulating material, provided with a capillary bore 1 I closed at one end, and at the other end connecting with the interior of the bulb l2, integral with the tube. The wall of the bulb is preferably thinner than the wall of the tube, so that upon excess pressure in the tube the bulb will be the first to rupture.

Intermediate its ends, the bore H is provided with a constriction l3. Contacts l4, l5, provided in spaced relation in the bore at each side of the constriction I3 are formed by the inwardly projecting ends of wires passing through and sealed in the wall of the tube. The contacts are normally connected by a column of electrical conductive fluent material, such as mercury, in the bore II and bulb l2. For all normal temperatures, the upper end of the mercury column is spaced from the upper endof the tube, as shown at [6.

The mercury is under a head pressure in the tube at normal temperature, the pressure being produced by a quantity of compressible vapor such. as nitrogen gas, trapped in the bore be tween the upper end of the column of mercury and the closed upper end of the tube. The gas trapped above the column is under pressure, representing the compression of a volume of gas that when free will more than fill the bore of the tube and the interior of the bulb.

To obtain this pressure, the gas may be introduced into the tube under pressure through its upper end, while the mercury in the bulb is cooled and the open end of the tube then sealed. Subsequently, upon the temperature of the mercury coming up to normal, the mercury rises in the tube, additionally compressing the gas. Rise of the mercury column due to temperature changes of the mercury, occasioned by normal atmospheric variations, are permitted by the space normally between the upper end of the column and the end of the tube.

Metal clips H for supporting the tube, are clamped in spaced relation to the tube by screws and nuts I8, and have outwardly extending portions which are secured by screws N, to an insulating mounting block 20, located at a point where an indication of temperature change is desired. The clips are connected electric lly wi h the contacts I 4, IS, in the bore of the tube, the wires ofthe contacts respectively clamped between the clips and the wall of the tube. Opposite lines of the circuit in which the thermostat is placed are connected to the clips with the lines clamped under the heads of the screws I9.

The tube may be located at any point where it is desired to have an indication of an abnormal predetermined rise in temperature, being placed, for instance, ina room of a building and connected in an electric circuitto break the circuit and cause an alarm to be sounded in case of fire.

When the temperature in the neighborhood of the tube rises to the predetermined degree, the mercury expands, decreasing the volume or the trapped gas, and increasing its pressure to a value that ruptures the bulb. The mercury isforcibly expelled from the tube by expansion of the gas trapped at the top of the mercury column, clearing the tube of mercuryand disconnecting the contacts] 4, l5, The flowof'the mercury, through the tube is deceleratedbygthe constriction l3 in the bore of the tube as the mercury passes the constriction. The constriction retards themercury from a' too,v rapid discharge, and thereby prevents the, 'creationof. a partial vacuumin the bore, whichwomd draw the mercury bacl; into the boreand possibly effect a bridging of the electric circuit terminals l4 and. I5.

,The use of pressure to expel the mercury from thethermostat makesit lpossible to use a tube having an exceedingly'small bore, requiring a minute quantity of mercury, and providing economy,' especially since the mercury is lost upon operation. The forceful expulsion of the mercury upon rupture otthe bulb assures a quick positivebreak of the @circuit, preventing arcing, ltheexpanding'gas effectively driving out the merwry,

Thegas pressure inthe capillary'borepermits the thermostat tobe placed in an inclined or invertedposition without disturbing the mercury column oreffecting operation' of the thermostat.

It also preventsparting of the column and guards against breaking of the circuit except when the ambient temperature reaches the predetermined value j The thermostat as a capillary tube has a bulb orinore fragile end ca'pable of being shattered by ade'te'rmineddegree of pressure'within the bore of the tube developed by the movement of the thermo-exp'ansive fluid within thebore at a determined degree of temperature to expelthe fluid from the tube tocontrol an electric circuit.

The tube is of miniature size and inexpensive to manufacture, so that its replacement, which is required to re-establish the electric circuit, can be made at a very nominal cost.

The thermostat is constant in maintaining the electric circuit at any temperature below a maximum degree, and its column height normally is not altered to uncover either of a pair of contacts for an interruption of the circuit, and there fore also may be used or inserted in an electric circuit to serve as a fuse.

Having described my invention, 1 claim:

1. A thermostat, comprising: a sealed capillary tube having a bulb at one end of a fragility to rupture upon the development of a predetermined pressure in the bore of the tube, a thermo-expansive electro-conductive fluid contained in said bulb and rising in a column in the bore of the tube, a pair of spaced electrodes traversing the tube and in constant electric-conductive connection through {the fluid in said bore under abnormal low degree"thermo-conditions for maintaining an electric circuit, the head end of the bore of the tube supplied with a vapor under pressure and compressive by the rise of the fluidcolumn thermally to a determined height to develop a pressure for rupturing the bulb and expel the fluid from thebore for breaking the circuit between the'ellectrlodes, the bore of the tube between the electrodes constricted for a control of the expulsion of the fluid when the bulb is ruptured to'assure a complete discharge thereof between the electrodes.

2. A thermostat, comprising a capillary tube having a bulbat one end thereof in communication with the bore of the tube, a thermo-expansive electro-conductive fluid in said bulb and extended to a determined column height in the bore of the tube,lthe bulb of a fragility to be ruptured by a determined degree of pressure developed upon expansion of the fluid column compressing a vapor charge supplied in the bore over the head end of the fluid column upon exposure of the tube to 'a determined degree of temperature, the bore constricted in proximity to the bulb and electric circuit electrodes extending within the tube respectively relatively disposed beyond opposite-ends of the bore constriction, and normally exposed to the thermo-expansive fluid to 

